When the flow rate of fluids is to be determined, it is of course desirable to determine the rate of flow in a reliable and reproducible manner. It has been particularly difficult to provide a single flow meter which can universally measure fluid flow where the flow can vary from a very low rate (e.g. in a pipe carrying a low viscosity fluid, or at low pressure) to a high rate, (e.g. in a pipe carrying a high viscosity fluid at high pressure). These types of widely varying conditions are often encountered by farmers applying various chemicals to their fields. As an example, farmers utilize a tank of liquid chemical or the like which feeds a plurality of tubes leading to field spray nozzles. The rate of flow of the chemical through a main feeder tube or through each of the sprayer tubes must be determined to enable the farmer to accurately determine the amount of chemical being applied per acre.
The fluid to be applied, and thus which must be metered, is often far from an ideal homogeneous liquid. The fluid may have microscopic suspended chemical particles, may be of high, low, or varying viscosity, may have metallic or other particles such as seeds of undetermined size suspended therein, may be highly corrosive, etc.
It is of course preferable that the farmer should not have to change fluid meters to accommodate the different conditions as noted above, and yet the meter should be easy to remove for servicing. The metering device should also reliably provide an indication of the flow rate in the presence of a hostile environment.